Assessment of Territory Value by a Tropical Hummingbird (Amazilia saucerottei)

Abstract

I investigated how a tropical hummingbird, Amazilia saucerottei, determines whether or not to defend a patch of Combretum farinosum and when to begin and end defense. Energetic value of a patch and number of flowers were not correlated through the period of flowering. First-day nectar production per flower declined from 68.11 J in late January to 19.07 J in early March. Patches of defended C. farinosum had a greater maximum number of nectar-producing inflorescences than did undefended patches. The threshold minimum number of nectar-producing inflorescences for defense decreased from 35 to 20 late in the flowering period. Defense began while the number of inflorescences producing nectar was below the threshold, indicating that birds assessed the patch's future value. The energetic value of a defended patch was the same at the beginning and end of territoriality (approximately 36 kJ), but the average number of nectar-producing inflorescences was twice as great at the end as at the beginning (11.6 vs 5.6), suggesting that birds asessed the value of the patch by direct measurement of energy intake. Daytime rate of energy expenditure estimated from time budgets was 0.545 J/sec. Total daily energy requirement was 34.14 kJ/day.